Improved determination ofd¯(x)−u¯(x)flavor asymmetry in the proton by data from the BONuS experiment at JLAB and using an approach by Brodsky, Hoye

Abstract

The experimental data taken from both Drell-Yan and deep-inelastic scattering (DIS) experiments suggest a sign-change ind(x) −ū(x) flavor asymmetry in the proton at large values of momentum fraction x. In this work, we present a phenomenological study ofd(x)−ū(x) flavor asymmetry. First, we extract thed(x) −ū(x) distribution using the more recent data from the BONuS experiment at Jefferson Lab on the ratio of neutron to proton structure functions, F n 2 /F p 2 , and show that it undergoes a sing-change and becomes negative at large values of momentum fraction x, as expected. The stability and reliability of our obtained results have been examined by including target mass corrections (TMCs) as well as higher twist (HT) terms which are particularly important at the large-x region at low Q 2 . Then, we calculate thed(x) −ū(x) distribution using the Brodsky, Hoyer, Peterson, and Sakai (BHPS) model and show that if one chooses a mass for the down quark smaller than the one for the up quark it leads to a better description for the Fermilab E866 data. In order to prove this claim, we determine the masses of down and up sea quarks by fitting to the available and up-to-date experimental data for thed(x) −ū(x) distribution. In this respect, unlike the previous performed theoretical studies, we have shown that this distribution has a sign-change at x > 0.3 after evolution to the scale of available experimental data.

Properties of structure functions from helicity components of light quarks and antiquarks in the statistical model

“…This means that the flavor asymmetry of the light antiquark distributions is the same for the corresponding helicity distributions, as noticed long time ago [12] (see also ref. [13]). Now let us come back to all these components xu + (x, Q 2 ), ...xū − (x, Q 2 ) and more precisely…”

Implementation of target mass corrections and higher-twist effects in the xFitter framework

“…For example, accurate knowledge of the u and d quark distributions at high x is very important at collider experiments in searches for signals of new physics at high Q 2 values. On the other hand, the flavor and spin dynamics of quarks in the nucleon can be explored by studying the large-x region, considering this fact that the d/u ratio at large x is very sensitive to different mechanisms of spin-flavor symmetry breaking [21][22][23]. It should also be noted that the accurate recognition and calculation of the QCD backgrounds in new physics searches at hadron colliders would not be possible without precise determination of PDFs at large x.…”

Study of the s−s¯ asymmetry in the proton

“…The first ones are produced perturbatively through the splitting of the gluons into qq pairs and are dominant at small x regions, while the later ones are produced through the nonperturbative fluctuations of the nucleon state to five-quark states or meson plus baryon states and are dominant at large x regions. In recent years, the intrinsic quarks have been a subject of study by many investigators [31,34,35,36,37,38,39,40,41,42,43,44,45].…”

“…However, it is significant only in regions of small momentum fraction x and also inconsiderable in magnitude, so that cannot describe the present experimental evidences for the s − s asymmetry. In this way, the nature and dynamical origins of s − s asymmetry (as well as the d − ū flavor asymmetry [31]) have always been an interesting subject to research both experimentally and theoretically (for a review see Refs. [32,33,34] and references therein).…”